Display apparatus



April 8, 1969 Rio. coB ET AL 3,437,869

DISPLAY APPARATUS Filed Nov. 1, 1965 Sheet ofS FIGW TRANSLATORTRANSLATOR FIG.5

INVENTORS RICHARD OICOBB RAYMOND A. SKOV ATTORNEY April 8, 1969 FiledNov. 1. 1965 DISPLAY APPARATUS Sheet 3 ors FIG. 3

l I 1 l x 50 1 4c 50 6C 1c) 3,437,869 Patented Apr. 8, 1969 York FiledNov. 1, 1965, Ser. No. 505,795 Int. C1. 1101 29/72 11.5. Cl. 315-18 8Claims ABSTRACT OF THE DISCLOSURE A display wherein X, Y input data inone number set is translated into another set X(A), Y(A); X(B), Y(B); orX(C), Y(C) having more orders and having symmetry around a centralposition defined by one of the additional orders. By a plurality of suchtranslations sharing the same central position, characters of differentsizes A, B, C can be drawn, each symmetrical about the central position.The character generator deflection is held at that relative positionduring non-character mode vector operation of the display, so thatcharacters, when later drawn on the vectors, will appear in centeredrelation thereon.

This invention relates to data processing systems, and more particularlyto a display system and data translating means forming a component ofthe same.

Display apparatus has been found useful in input-output devices in dataprocessing or handling systems. For example, in a cathode ray tubescanner or display apparatus, the beam of the tube may be deflectable todigital addresses on the tube screen for executing vectors which (whenunblanked) yield traces defining a desired configuration. Thisconfiguration may be an arrangement of lines constituting a drawing, orit may be a character (alpha, numeric, or arbitrary symbol), or it maybe a time-interleaved and positionally overlayed combination of the two.

The exact position of the character may be of some importance. Forexample, in an input drawing-scanner apparatus, a line follower symbolmay be projected onto a drawing in such a manner that it is, desirably,centered on a predicted position on the line. In a display of a familyof curves, each may have symbols thereon (e.g., identifying the same)which, desirably, are centered on the corresponding curve. In a displayhaving a special symbol which is to be sensed by a manipulatablephotocell device (such as a light gun or a light pen) or wherein such asymbol is merely indicative of some operator input (such as in a joystick or voltage pen type of device), the special symbol is, desirably,centered on a known cordinate.

Moreover, in each case there are occasions when it Would be desirable tochange the size of the character without changing its center. In thisway the character may be larger or smaller but still have predetermined,perfect centering on a predetermined position on the display or scanningfield.

A usual means for generating characters in a display (or scanner) deviceis to provide incremental deflection for the electron beam whereby thebeam is made to follow a prescribed path in terms of deviations fromsome position defined by the main deflection system. In digital systemsthe available increments are definite units in a dimensional field whichmay have no addressable center. For example, in a three-bit (i.e., threeorder) binary system the addressable positions (in decimal) for each ofX and Y in the dimensional field are 0, 1, 2, 3, 4, 5, 6 and 7. Thecenter would be X=3.5, Y=3.5, which is not addressable.

A difficulty therefore arises in attempting to draw characters which areperfectly centered on a display address. If the character deflectionsystem is kept at its zero X, zero Y condition during the drawing of thedisplay, superposed characters will be completely off-centered withrespect to a line which has been drawn by the display since the lowerleft hand corner of the character will be the point of origin by whichthe display is drawn. If some other character input is utilized duringthe drawing of the display, characters will inherently be ofl centerbecause of the above noted fact that in a binary system the center of adeflection system such as a character deflection system is inherentlyoff center. Moreover, this off centered relationship becomes aggravatedas the character is expanded.

The prior art contains examples of means for relocating and expandingportions of a display, but these prior art techniques do not completelysatisfy the need to which the present invention is addressed. Forexample, US. Patent No. 3,011,164 shows a display apparatus whereinbinary data in a given set are given changed weights, with certainorders being complemented to give the eflect of two way expansion aboutone of the orders. In another prior art example, a disclosure authoredby J. W. Carlson entitled, Display Centering and Expansion Apparatus,published in the IBM Technical Disclosure Bulletin, vol. 5, No. 11,pages 89-91 (April 1963), there is shown a data manipulating systemwherein a new origin is selected by subtraction of a certain value andthen the display is expanded by order weight alteration (shifting). Ofcourse, expansion is also possible by simple analog amplification.

In each of the above prior art examples, the data is expanded about someaddressable point to some other point in the same scale system, be itdigital or analog. Given a binary input which is inherentlynon-centered, such a display is centerable only by use of a bias, whichbias must then be changed with each level of expansion. Moreover, theabove cited prior art does not deal with changes in mode of operationfrom character to non-character mode in order to form superimposedimages.

In accordance with the present invention, means are provided wherein aset of input data is translated into another set having more orders andhaving symmetry around a position, hereinafter called the Home Position,a position defined by one of the additional orders. Moreover, means areprovided affording a plurality of such translations having diflerentscale factors and sharing the same home position. The result is that theinvention enables the generation of a character which is perfectlycentered on a home position and therefore is perfectly centered on adisplay element which has been drawn while the character control is inthat home position. Moreover, the invention provides unchanging symmetryabout that center with change in size of the character drawn thereabout.Finally, these advantages are carried out by simple, accurate, digitalmanipulation.

Accordingly, it is a primary object of the invention to provide, in adata processing apparatus, improved means for executing controlleddeflections of an electron beam or similar display or scannerinstrumentality.

It is another object of the invention to provide apparatus as aforesaidmeans defining an operative deflection field or grid for an electronbeam for operation of the apparatus in a character generating mode, withthe grid having a true center rest position providing an operativeaddress at which the character deflection system is held during otherdeflections of the electron beam in non-character mode, so as to yieldin character mode characters which are perfectly centered on a displaydrawn in noncharacter mode.

Still another object of the invention is to provide, in an apparatus asaforesaid, a data translation system wherein a set of digital inputinformation is translated into another set having more orders forenabling symmetry and symmetrical expansion.

Yet another object of the invention is to provide the above features byuse of simple, accurate, digital circuitry.

The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of a preferred embodiment of the invention, as illustratedin the accompanying drawings.

FIG. 1 is a diagram of a data processing system including one preferredembodiment of the invention.

FIG. 2 is a schematic diagram of a translator circuit representative ofa part of FIG. 1.

FIG. 3 is a diagram showing related deflection grids which show theoperative ranges of deflection of an electron beam resulting from theoperation of translator circuitry of FIGS. 1 and 2.

FIG. 4 is illustrative of a display such as may be generated byoperation of the apparatus of FIG. 1; and

FIG. 5 is a detail showing steps in generation of display indicia of thegeneral kind seen in FIG. 4, as related to an operative grid system ofFIG. 3.

Referring more particularly to FIG. 1, the invention may be embodied ina data processing apparatus comprising a central processor unit orcomputer having an output apparatus including a cathode ray tube 12. Inthe illustrated embodiment, the cathode ray tube 12 is pro vided withmain XY deflection yoke having windings 14, 16, and a secondary orcharacter yoke having additional X and Y windings 18, 20, hereinaftersometimes referred to as the AX and AY deflection coils. The deflectioncoil arrangements may be of the kind wherein each deflection coil hastwo halves in which the currents flow in relative opposition so thatwhen there are equal currents there is no deflection. Such a windingarrangement may have three connections for each coil, represented in thedraw ing by the line groups 22, 24, 26 and 28. It will be understoodthat this connection arrangement is representative only; for example, insome systems the common connec tion to the two halves of each deflectionwinding is actually two wires for enabling use of certain additional balancing or surge drive networks or the like.

The several line groups are driven by digital to analog converter anddriver circuits 30, 32, 34, 36, the main deflection driver circuits 30,32 being under the control of the central processor unit 10 via inputcables 38, 40, and the character deflection driver circuits 34, 36 beingunder the indirect control of the central processor unit .10 via, in theillustrated embodiment, a character generator 42 together with digitaltranslator circuits 44, 46 of the invention.

The input signals to the translator circuits 44, 46 on cables 48, 50could be provided directly from the central processor unit, but thecharacter generator 42 is shown because such an apparatus isadvantageously included in display systems for removing some of theburden of steps in character generation from the central processor.Accordingly, the central processor may provide digital commands onoutput cable 52 which identify the character to be generated, and thecharacter generator 42 may contain circuitry which thereupon issuesseries of digital signals on its output cables 48, 50 for execution ofparticular strokes of the electron beam of the cathode ray tube 12, byoperation of the character yokes 18, thereof, so as to trace the desiredcharacter on the face of the cathode ray tube. Ordinarily, suchdeflections are minor in extent compared to the face 54 of the tube andaccount only for the configuration of the character. The placement ofthe character on the face is effected by operation of the maindeflection yokes 14, 16 and the control circuitry leading thereto.

As will be dealt with more fully hereinafter, the apparatus may haveboth character and non-character modes of operation, and during anon-character mode of operation, the dynamic operation of the electronbeam may be solely under the control of the main deflection yoke 14, 16,with the character yoke 18, 20 held in a steady state condition.Conversely, in character mode, the character yoke may have dynamicdeflection control while the main yoke is at a steady state. In eithercase, there are occasions when it is desirable to blank the operation ofthe electron beam so as to enable adjustments of the position thereofwithout efiecting a trace. Such a blanking control is indicated as S6and is shown to be operative in response to a logical OR circuit 58under selective control of the central processor unit 10 or thecharacter generator unit 42 via lines 60, 62, as may be required duringoperation of the apparatus. It will be understood that this blankingcontrol 56 may be operative in any conventional manner, such as byoperation of the control grid of the cathode ray tube (not shown), andthat the cathode ray tube may be fitted with other conventional partsand connections such as anode and focusing connections and the like,also not shown.

In the illustrated apparatus the signal translation circuitries 44, 46are operative to serve three main functions. First, they provide signaloutputs on cables 64, 66 which are operative to provide a Home Positionof which is at a precisely known location within and preferably near thecenter of the deflection capability of the AX and AY deflection windings18, 20. As will become apparent hereinafter, it is at this Home Positionthat the character deflection system is held during the non-charactermode of operation of the device. Secondly, the translator circuits 44,46 provide ranges or sets of outputs symmetrically disposed about theaforesaid Home Position for enabling the generation of characters whichwill have a true center on that Home Position and therefore can be trulycentered on a desired position in the display generated duringnon-character mode. Thirdly, the translator circuits 44, 46 provide forgenerating a plurality of such sets of output signals having differentscale factors that the aforesaid character can be made to have differentsizes. Accordingly, inputs to the translation circuits include acharacter mode-non-character mode command line 63 and character sizeinformation lines 70, 72, in addition to the character form informationOn cables 48, 50.

Since the translator circuits 44, 46 of the system of FIG. I may beidentical, only one of them, the X signal translator circuit 44, isshown in detail in the drawings. This circuit is shown in FIG. 2 and maycomprise a size input register for storing input signals received fromthe central processor unit 10 via lines 70, 72. In the illustratedapparatus, provision is made for three sizes of characters hereinafterreferred to as the A size, the B size, and the C size. In a binarysystem, two orders or bits of information are needed to define the threepossibilities and therefore the register 80 has two inputs 70, 72 andtwo outputs 82, 84. The levels on lines 82, 84 are decoded in aconventional manner in a circuit 86 to yield a unique output on one oflines 88, 90, 92 corresponding respectively to the three sizes of whichthe apparatus is capable. Cable 48 contains lines corresponding to threebinary orders identified in the drawing by the decimal notation 1, 2, 4,as shown. The three orders enable the communication of values of 000through 111 in binary notation, or 0-7 in decimal notation. Althoughthere are only three binary orders of inputs in the cable 48, there aresix binary orders of outputs in the cable 64, as indicated by thesymbols D1 through D32 representing the weights of driver current in thecorresponding AX D/A converter 34 which are activated by those lines.

The translator circuit 44 includes a matrix by which the three bit inputto six bit output conversion is made in accordance with the sizeinformation provided on the size indicator lines 88, 90, 92. This matrixis activated only during character mode of operation of the devices.Therefore the character-non-character line 68, which is assumed to be upor have a significant signal during noncharacter mode in the presentapparatus, is connected through an inverter 94 to the conditioninginputs of AND gate circuits 96, 98, 100 to admit the signals from thedecoder 86 to the translator matrix only during character modeoperation. Thus, during size A character mode operation, matrix ANDcircuits 102, 104, 106, 108 are conditioned. During size B charactermode operation matrix, AND circuits 110, 112, 1.14 are conditioned.During size C character mode operation only AND circuits 116, 118 areconditioned.

The outputs of this matrix are then ORed via circuits 120, 122, 124, 126to the respective binary order lines of cable 64, in the manner shown.However, the highest order output line in the cable 64 is not energizedfrom the aforedescribed AND circuit matrix. Rather, it is energizedthrough an OR circuit 128 directly from the high order, 4 weight inputline .130 of the cable 48. This input is utilized also through aninverter 132 which yields afnot 4 output on line 134 to energize oneinput of AND circuits 102, 104, 110, as shown. The D32 or high orderoutput line in cable 64 is also energizable through an input 136 whichis up or on during non-character mode operation. As will be seen morefully hereinafter, this results in the provision of deflection to theHome Position during non-character mode operation of the translatorcircuit.

FIG. 3 in conjunction with Table I and II is illustrative of theoperation of the translator circuit of FIG. 2. The X (C) and Y(C) axisare marked, as referenced for example at 140, with small intervalscorresponding to the smallest deflection executable by the AX or AYdeflection coil system by and upon a lowest order increment of the sixbit signal on cable 64 or on cable 66, respectively. In FIG. 2, thisincrement results by and upon the change of 1 to 0 or 0 to 1 in thevalue of the signal on the lowest order output line D1 of the circuit.The coordinate values 0C through 7C along the X(C) and Y(C) axescorrespond, in size C, to the 0 through 7 values at the input of the Xtranslator circuit 44 (FIGS. 1 and 2) and its companion Y translator 46(FIG. 1), respectively. Since there are three sizes available, theseinput values 0-7, 0-7 are seen three times on different scales in FIG. 3to form three grids, the A grid, the B grid and the C grid correspondingto size A, size B and size C. To avoid crowding in the drawing, only theY axis values are shown in size A.

The center position 142 common to each'of the grids is the HomePosition, which is a position that is non addressable, that is,corresponds to a value of 26:35, Y=3.5 in each of the grids. This valuecannot be represented numerically by the three bit signal input to thematrix of FIG. 2. However, the Home Position is utilized duringnon-character mode of the device, and is definable by the six bitoutputs of the translator circuits 44, 46, as a value in each of X and Yof 100000 in binary or weight D32 in decimal.

Table I shows the decimal equivalents of the translator inputs, as usedin FIG. 3 and Table II. Table II summarizes the operation of thetranslator 44 or 46. As will be seen in Table II, 0A through 7A, 0Bthrough 7B, and 0C through 7C comprise sets bearing a 1, 2, 4 sizerelationship which have been fitted to the binary capability of theoutput of the circuit of FIG. 2 in such manner that each issymmetrically disposed about the Home Position.

TABLE I Input Decimal Binary (48, 50) Equivalent (X, Y)

111 HOME (CM) TABLE II Input Input Output Output Size Code Size Code A BO A B 0 CM-HOME (3.5) 100000 000000 In Table II, the six bit binarycoded output has order positions, reading left to right, of thirty-twoweight, sixteen weight, eight weight, four weight, two weight, and oneweight. Binary signals on lines D32 through D1 in cables 64, 66 arecommunicative of these values to the corresponding converter 34, 36. Theconverters 34, 36 may be of the kind having a binarily weighted currentdriver for each order, selectively connected to one half of thecorresponding yoke winding 18, 20 or the other. Thus, for example, asignal of D32 alone in each of AX and AY would yield thirty-two units ofcurrent in one half of each of windings 18, 20 opposed by thirty-oneunits in the other halves, resulting in a net deflection of plus oneunit in each of AX and AY or Home Position.

FIG. 4 shows the result of the Home Position-character grid orientationsof FIG. 3 and Table 11. Let it be assumed that the data processingapparatus of FIG. 1 is to be used to portray on the face of the cathoderay tube 12 a display comprising a family of curves 150, 152 on acoordinate axis system 154, 156, and that the curve is to have displayedon it one or more representations of a symbol such as a square 158, andthe curve 152 is to have a diflFerent symbol such as shown at 162, 164.Such symbols may be utilized to identify the curves in the family ofcurves or to show the positions of experimental data from which thecurves were drawn. In either case but particularly in the latter case itis highly desirable that the symbols be centered on the curve, that is,that they be drawn symmetrically about a home position falling on thecurve.

Moreover, it is further highly desirable that if these symbols arechanged in size that they not change in position; namely, that theymaintain the same Home Position. This is illustrated in the case of acircular symbol 166 such as is sometimes used as a symbol indicative ofa light gun or light pen operative position. In the operation of such adevice it is sometimes desired to have the symbol be larger or smallerwhile maintaining the same data-significant position. This is enabled bydrawing the symbol 166 in larger versions such as indicated at 168 or170 about the same Home Position in accordance with the operation of theinvention.

Although the curves 150, 152 in FIG. 4 appear to be smooth lines, onemeans of producing such curves, frequently used in digital apparatus, isto deflect the electron beam by operation of the main yoke coils 14, 16through a succession of vectors. This is done by operating the digitalto analog converters 30, 32 in accordance with a succession of valuesfed to them from the central processor unit 10 through the connectingcables '38, 40. Since the main yoke coils 14, 16 may be operative todeflect the electron beam throughout the entire extent of the face 54 ofthe cathode ray tube, the main deflection signals on cables 38, 40 aredesirably of high resolution, such as the ten bit signals indicated inthe drawing.

It will be understood, however, that no matter what the main deflectionX, Y may be, there is added to this deflection the AX, AY resulting fromoperation of the character yoke deflection coils 1'8, 20. Since thedeflect-ion imparted by these coils is held at the Home Position of thecharacter yoke during non-character mode, the character yoke imparts nodistortion to the noncharacter made generated display. However, in theillustrated embodiment of the invention it does impart a small constantdeflection to the electron beam (a small bend in the electron beam) ofthe cathode ray tube. This results from the fact that the inputs to theAX and AY digital to analog converters 34, 36 which would correspond tono deflection by the character yoke would be not 100000, 100000 but onehalf a unit of the lowest order in each of X and Y less than that, avalue which would be unobtainable in a binary system but is very closelyapproached in the six bit system illustrated. This slight deflectioncould be biased out but it is ordinarily so unimportant that this is notrequired. It produces no distortion in the non-character mode display(e.g., 150, 152, 154, 156) because it is present in the Home P- sitionduring the generation of those elements.

FIGURE 5 is illustrative of the operation of the main and characteryokes of the illustrated apparatus during change from non-character modeto character mode and then back to non-character mode. Let it be assumedthat the apparatus is in non-character mode and has just finishedexecution of a trace 180. Since the character yoke coil 18, are alwaysenergized with a D32 input corresponding to Home Position when theapparatus is in non-character mode, the center of the invisiblecharacter grid (the Home Position) will be at the end of the vector 180.Let it be assumed that the next command in the program of the centralprocessor unit 10 is to draw a circle around the end of the vector 180.The central processor units sends an eight bit command to the charactergenerator 42 via cable 52 defining the shape of the character to beexecuted, namely, a circle. The

CPU 10 also sends on line 70, 72 the size code for the circle to beexecuted, and shifts the level on line 68 to its down or off conditionthereby signalling the change from non-character mode (OM) to charactermode (CM). Let it further be assumed that the character generator 42terminates each character with an output on cables 48, 50 of 000,000corresponding to the lower left hand corner of the character grid (nomatter what its size).

Referring to FIG. 2, there will therefore be a zero significant or downsignal on all three lines of cable 48, and when the signal on line 68goes down, OR circuit 128 will become deconditioned and AND circuits9'6, 98, 100 will become conditioned. If the size command on line 70,7-2 dictates size A, outputs D1 and D8 will be up. If size Bisspecified, outputs D1 and D16 will be up. If size C is prescribed,output D4 alone will be up. Accordingly, no matter what size charactergrid is prescribed the position of the electron beam will be deflectedto the lower left hand corner of the prescribed character grid, orcharacter grid address 0,0 in decimal. This will result in the blankedadjustment of the electron beam position indicated by FIG. 5 by thedotted vector from position 315, 3.5 to 0,0. The blanking of theelectron beam during this time could be 8 under the control of thecharacter generator 42 via line 62 or the control of the CPU via line60, it being assumed in this discussion that it is under the control ofthe CPU via lines 60 as a part of the programmed change fromnon-character mode to character mode.

The first step of the operation of the character generator 42 is tochange its output from 0, 0 decimal equivalent to 0, 2 decimalequivalent while maintaining the cathode ray tube blanked by operationof an output on line 62. This then executes a blanked repositioning asshown by the dotted vector from 0,0 to 0,2 in FIG. 5. The next step inthe operation of the character generator is to change its output from0,2 to 0,5 while unblanking the electron beams by operation of line 62(the signal on line 60 having been previously dropped when the charactergenerator was put into operation) so as to execute the visible tracefrom 0.2 to 0.5 in FIG. 5. Subsequent steps of operation of thecharacter generator feed new vector endpoint values of 2,7; 5,7; 7,5;7,2; 5,0; 2,0 and 0,2 in succession to execute the corresponding visibletraces as seen in FIG. 5. This results in a generally circular figurehaving the Home Position of 3.5, 3.5 at its exact center.

It will be seen that a three bit binary code (0-7 decimal) providessufficient flexibility to enable the generation of reasonably smoothlyshaped characters; of course if greater flexibility is desired more bitscould be used at the cost of more elaborate circuitry. It will beunderstood that, with the circuitry shown, the larger circles 168 and170 in FIG. 4 would show as octagonal approximations of circles althoughthis would not be so obvious in the small circle 166. However, in everycase the center of the figure would be exactly in Home Position andtherefore exactly on the trace 1'50.

Returning to FIG. 5, and following the previously stated assumption thatthe character generator is one which returns to 0,0 decimal output(000,000 binary) at the end of each character, the final operation ofthe character generator would be to execute a blanked trace from 0,2 to0,0 as seen by the dotted vector in FIG. 5 between those positions.

If the CPU 10 was programmed to return to noncharacter mode so as tocontinue on with a trace 182 by operation of the main deflection system,the signal on line 68 will be brought back up, resulting in thedeconditioning of AND circuits 96, 98 and 100 in translator 44 as wellas the corresponding circuits in translator 46, so as to return theoperation of the output of the translators to D32 in each case,corresponding to the Home Position. If the CPU 10 blanks the electronbeam by operation of an appropriate signal on line 60, this beamadjustment to the center of the character grid will not be seen, andthis blanked readjustment is indicated by the dotted trace between 0,0and 3.5, 3.5 in FIG. 5. With the character yoke 18, 20 again adjustedfor Home Position, operation of the electron beam can be unblanked andthe main yokes 14, 16 operated to preceed to draw a trace along path182. The aforedescribed operation will have resulted in drawing theoctagonal circle shown in FIG. 5 exactly centered on the continuous line180, 182.

As explained above, the small deflection introduced by the characteryoke and Home Position introduces no distortion in a visual display.When the invention is used to produce a line following symbol foranalyzing some other graphic input such as a drawing, that graphic inputcan be maintained in such position as to compensate for that deflection.

Thus, while the invention has been particularly shown and described withreference to preferred embodiments thereof, it will be understood bythose skilled in the art that the foregoing and other changes in formand details may be made therein without departing from the spirit andscope of the invention.

What is claimed:

1. In a digital data display system having a display delineating deviceand non-character and character modes of operation of the same,

deflection means for controlling the movement of said delineatingdevice, said deflection means including a data translating means toconvert input data thereto of one number set into a second number set,

said second set being characterized by symmetry around a predeterminedvalue in said second set not present in said one set,

and means for holding said translating means at said predetermined valueduring non-character mode of operation of said system,

whereby displays can be generated in said non-char-- acter mode inposition for registry with the centers of characters generated throughoperation of said translating means.

2. Apparatus in accordance with claim 1 wherein,

said translating means comprises means to selectively convert said inputdata into said second set and an additional set having a differentextent about said predetermined value,

whereby a change in size of a character delineatable by said device iseffected.

3. In a digital data display system having a cathode ray tube andgraphic and character modes of operation of the same,

deflection means for controlling the movement of an electrom beam,

said deflection means including -a binary data translating mean-s toconvert input data thereto of a first set of values into a second set ofvalues having more orders than said first set,

said second set including a predetermined value not included in saidfirst set,

and means to set and hold said translating means at said predeterminedvalue during graphic mode of operation of said system,

4. Apparatus in accordance with claim 3 wherein,

said translating means comprises logical matrix means to selectivelyconvert said input data into said second set and an additional sethaving a different extent about said predetermined value,

whereby a change in size of a character delineatable by said device iseifected.

5. Apparatus in accordance with claim 3 wherein,

said input data to said translator comprises three binary orders andsaid second set comprises the input data plus three lower orders.

6. Apparatus in accordance with claim 3, wherein said input data to saidtranslator comprises three binary orders and said second set comprisesthe input data plus three lower orders,

said translating means comprises means to selectively convert said inputdata into said second set and an additional set having a diflerentextent about said predetermined value,

whereby a change in size of a character delineatable by said device iseffected.

7. Apparatus in accordance with claim '6, including control means forswitching between graphic and character modes of operation and separatedata channels for each.

8. In a digital data display system having a display delineating deviceand non-character and character modes of operation of the same,

deflection means for controlling the movement of said delineatingdevice,

said deflection means including primary deflection signal means toetfect non-character mode display traces and supplementary signal meansto efiect character delineating display traces for superposition on saidnon-character traces,

said supplementary signal means including a data translating means toconvert input data thereto of one number set into a second number set,

said second set being characterized by symmetry around a predeterminedvalue in said second set not present in said one set,

and means for holding said translating means at said predetermined valueduring non-character mode operation of said system.

References Cited UNITED STATES PATENTS 3,256,516 6/1966 Melina et al.340324.l X 3,267,454 8/1966 Schaaf 340324.l 3,281,822 10/ 1966 Evans.3,293,614 12/1966 Fenmore et al. 3,325,802 6/1967 Bacon 340324.1

RODNEY D. BENNETT, Primary Examiner. BRIAN L. RIBANDO, AssistantExaminer.

US. Cl. X.R. 340-324.l

